Control circuit for setting phase shifters in scanned antenna array

ABSTRACT

According to the present disclosure, apparatus and process is provided for controlling delay devices in antenna elements of antenna arrays for controlling the direction of propagation of electromagnetic radiation. An analog signal is developed from a digital signal and operates on a first control device in a predetermined manner. The analog signal is subsequently altered, as by altering the digital signal in a binary adder, and the altered analog signal operates on the next control device. The control devices are arranged in sequential relation and are successively operated by a clock.

United States Patent 13,ss2,9s3

[72] Inventor Glen Martner 3,324,452 6/1967 Brightman et al. 343/854Monterey Park, Calif. 3,387,301 6/1968 Blass et al. 343/854 [2]] Appl.No. 831,501 3,500,412 3/1970 Trigon 343/854 gg 13:2? PrimaryExaminer-Eli Lieberman [73] Assignee Aerojebceneml CorporationAttorneys-Edward O. Ansell and D. Gordon Angus El Monte, Calif.

[54] CONTROL CIRCUIT FOR SETTING PHASE SHIFTERS IN SCANNED ANTENNA ARRAY7 Claims, 6 Drawing Figs.

ABSTRACT: According to the present disclosure, apparatus [52] US. Cl343/854, and process is provided for controlling delay devices in amem333/24-1 na elements of antenna arrays for controlling the direction of[51] f Cl Holq propagation of electromagnetic radiation. An analogsignal is [50] Fleld of Search 343/777, developed from a digital signaland operates on a first comm] 854; 333/24" device in a predeterminedmanner. The analog signal is subsequently altered, as by altering thedigital signal in a binary [56] References Cited adder, and the alteredanalog signal operates on the next con- UNITED STATES PATENTS troldevice. The control devices are arranged in sequential 3,205,501 9/1965Kuhn 343/854 relation and are successively operated by a clock.

('5') L44 I. t

4 A24. AP. 45

45f cuRRENT cuRRENT cuRRENT T GENERATOR GENERATOR GENERATOR CLOCK PULSEI 1 G E N ERAToR J 1 1 v" DIGITAL-TO-ANALOG CONVERTER /55 55 57 jSTORAGE REGISTER MV 5/ J as r '66 {29 52 (c HHS 56 BEAM AM POSITIONBINARY ADDER bc ETEP I55 INPUT 5 M INPUT (9) CLOCK CONTRQL (IIRCUTT FORSE'ETKNG PHASE SHHFTERS IN StCANNED ANTENNA ARRAY This invention relatesto control networks, and particularly to control networks forcontrolling current operable delay mechanisms for phase control antennaelements of antenna arrays.

lf signals to be propagated are fed simultaneously to each antennaelement of a linear array, each element will propagate electromagneticradiation at the same phase as the radiation generated by every otherelement, and a narrow pencillike beam of electromagnetic radiationhaving planar phase fronts will be propagated in a direction normal tothe array. However, it is often desirable to shift the direction ofpropagation of such electromagnetic radiation so that it is oriented atsome other angle to the array. Such directional controls are oftenperformed by means of phase shifters or delay networks associated witheach antenna element to delay the signal propagated by each element byan incremental amount so that the total propagated signal will be anarrow pencillike beam of electromagnetic radiation having planar-phasefronts, but directed in a direction at some angle to the array.Heretofore, the phase shifters or delay networks have been currentoperable phase shifter coils, the control of which has ordinarily beenaccomplished by to provide control apparatus for antenna arrays wherebythe current to each phase shifter is automatically controlled inaccordance with the desired propagation direction.

Another object of the present invention is to provide apparatus foradjusting coil so that the phase shifter will shift the phase of therespective propagated signal by an amount dependent upon the currentimposed on the shifter coil. The current for each phase shifter isordinarily calculated by means of complex trigonometric calculations andwas adjusted for each phase shifter separately. Since most antennaarrays have many elements and associated phase shifters, a considerableamount of time and equipment are required to adjust the current to eachphase shifter for each desired beam position.

It is an object of the present invention is to provide apparatus foradjusting the phase shift of each of a plurality of phase shifters foran antenna array, which apparatus is capable of changing the directionof propagation of electromagnetic radiation from the array by means of asingle adjustment.

In accordance with an optional desirable feature of the presentinvention the current generators are arranged to sequentially drive eachother and a clock is provided so that the current will be regulatedperiodically.

According to another optional desirable feature of the presentinvention, the analog source comprises a digital-toanalog converterwhich is driven by a digital adding mechanism. A signal, whose value isdependent upon the desired direction of propagation, is imposed upon thedigital adder which in turn drives the digital-to-analog converter. Therelationship between the converter and the adder is cyclic so that thephase shifts will be sequentially correlated for each antenna element ofthe array.

The above and other features will be more fully understood from thefollowing detailed description, and the accompanying drawings, in which:

FIG. 1 is an illustration of a typical linear antenna array forpropagating electromagnetic radiation;

FIGS. 2a through 2d are illustrations of pulse signals which illustratethe principle of operation of the present invention; and

FIG. 3 is a schematic block diagram of a circuit in accordance with thepresently preferred embodiment of the present invention.

The present invention is particularly useful in controlling the phaserelationship between the phase shifters of each microwave antennadisclosed in the copending application of Chalfin et al., Ser. No.792,070 for Antenna Array" filed Jan. 17, 1969, and assigned the sameassignee as the present invention. in the aforesaid copending patentapplication there is described an antenna array for propagating a narrowpencillike beam of electromagnetic radiation in a desired directionwherein a plurality of linear antenna arrays are mounted adjacent therim of a lens so that upon rim-feeding the lens a fan beam ofelectromagnetic radiation is propagated to the linear antenna arrays.Each array includes phase-shift means for effectuating the desired phaseshift for each radiating antenna element on the respective antennaarray. The phase-shift means disclosed in said Chalfin copending patentapplication comprises a ferrite core disposed in a wave guide and a coilwrapped around each of the cores. A direct current of preselectedmagnitude is passed through the coils to alter the phase velocity of theelectromagnetic radiation propagated by the waveguide. The presentinvention is directed particularly to the apparatus for selecting themagnitude of direct current for the coils for each ferrite phase shifterdisclosed in said Chalfin et al. application. it is to be understood,however, that the present invention is useful for other types of currentor voltage operable phase shifters.

in HQ 1 there is illustrated a linear array 10 of antenna elements A toA Each antenna element, which may, for example, be a dipole antenna, isconnected by means of cable 11 to a suitable signal source 14. Eachantenna element is capable of propagating electromagnetic radiation 12.As illustrated in FIG. 1 electromagnetic radiation 12 is beingpropagated in a direction k and contains planar phase fronts 13 disposedat an angle 6 from the plane of the array. (lt is to be understood thatthe direction k along which the electromagnetic radiation is propagatedis also disposed at an angle 6 from a line normal to the antenna array.)The distance between each phase front is illustrated by distance d.

For a linear array of antenna elements, it can be shown that adjacentantenna elements (n r A being equal to the distance between elements nand the reference point), and dis the distance between element n and aphase front. The phase shift required for a given antenna element can bedetermined from the expression:

where D,, is the phase shift required for element n and k=2rr/)t (3Hence, from equations (1 (2 and (3 It can be shown that a trigometricfunction of an angle which is greater than 360 (21:- radians) is equalto the trigometric function of the amount by whichthe angle exceeds amultiple of 360.

Put another way,

where m is an integer equal to the number of 211 radians in the angle(a-i-Z m). Applying this concept to the phase shift, it can beunderstood that if the phase shift exceeds 211' radians, the phase shiftnecessary for each antenna element can be expressed by Atb, I -21rm (5where m is the number of 21r radians in d Hence,

Thus, if an array of nine antenna elements (numbered (0- -8, element 0being the reference point) are intended to propagate a signal in adirection 30 from the normal to the array (=30), and if the antennas arespaced one wavelength apart (r=l from equations (4) and (6), thefollowing can be tabulated:

TABLE I The current necessary to drive a phase shifter to obtain thedesired phase shift can be determined by the following expression,

where 1,, is the current driving element n, and a is the currentnecessarv to obtain a 211 radian phase shift (expressed inmilliamperes). In the example, the current necessary to drive eachsuccessive phase shifter may be determined from equation (7) as phaseand current relationship of element 0-8 are (for a 30 propagationangle):

FIG. 2 is a graphic illustration of the relationship between the currentnecessary to drive the phase shifters and the angle of propagation 0. InFIG. 2a, there is illustrated the relationship between the propagationangle 0 and the current necessary for obtaining the phase shift b forangle 0 for an antenna array having antenna elements A, through A,, toinclusive, spaced r distance apart. The current necessary to obtain a360 (211') phase shift for the particular phase shifters is a directcurrent having a value a. Heretofore, an antenna designer would userectangular coordinate graph paper so sized as to relate the spacingbetween the antenna element to the current necessary to obtain a 360phase shift. The designer would plot the desired angle of propagation 0on the graph paper, in a repetition, sawtooth form 20 having itslowermost portion coincident with zero current and its peaks coincidentwith maximum current a. The point of intersection of graph 20 with thelines representing the position of the antenna elements A, through Awould then be related to the value of the current necessary to obtainthe particular desired angle of propagation 0 The designer would thenindependently establish the desired current for the phase shifterassociated with each antenna element, the representative currents beingillustrated at 21 in FIG. 2b. The difference in current AI betweensuccessive phase shifters could likewise be obtained from the graph.

If the designer desired to alter the angle of propagation 0, he had toreplot a sawtooth wave 22 at the new angle 0 (FIG. 2c) and obtain thecurrent values 23 as illustrated in FIGS. 2d.

The present invention is concerned with apparatus for automaticallyobtaining the current necessary for the phase shifters for such anantenna array. The apparatus in accordance with the preferred embodimentof the present invention is illustrated in FIG. 3, and includes a beamposition input 29 connected to binary adder 30 through input 31. Adder30 has an output 32 which provides an input to storage register 33. Theoutput 34 from storage register 33 provides an input to digitalto-analogconverter 35. Also, the output from storage register 33 is connected toinput 36 of binary adder 30. The output 37 from digitaI-to-analogconverter 35 is connected to the inputs 38, 39, 40, etc. of each currentgenerator I, 2, n. Each generator is operable to control the flow ofdirect current through a respective winding 41, 42, 43, etc. betweenpositive lead 44 and ground 45. Each current generator is connected bymeans of lead 46,46 to ground 45. The current generators l, 2, n arearranged in a shift register-type circuit so that operation of currentgenerator 1 provides a signal on lead 47 to enable operation of currentgenerator 2, and operation of current generator 2 provides a signal onlead 48 to enable operation of the next current generator.

Clock-pulse generator 49 has its output 50 connected to input 51 ofstorage register 33. Also, the output of clock-pulse generator 49 isconnected to inputs 52, 53, 54, etc. of the current generators.

A beam step input clock 55 is connected by means of lead 56 tosingle-shot multivibrator 57 which in turn is connected via lead 58 tothe first current generator to enable operation of the currentgenerator.

In operation of the circuit illustrated in FIG. 3, beam position input29 provides a digital signal b whose value is indicative of the desiredangle 0 of propagation of electromagnetic radiation from the antennaelements A, and through A,, inclusive. Signal b preferably comprisesbinary bits. Binary adder 30 adds the digital signals appearing atinputs 3] and 36 and delivers the resultant digital signal which maycomprise binary bits, to storage register 33 by means of output 32.Clock pulse generator 49 produces a pulse to enable storage register 33to accept and store the digital signal from adder 30. The digital signalstored in register 33 is delivered to digital-to-analog converter 35through output 34. Digital-to-analog converter 35 produces, at output37, a voltage having a value representative of the digital signalreceived from storage register 33. Also, the output from storageregister 33 is applied to the input 36 of binary adder 30 so that binaryadder 30 adds the signal be (which, as will be more fully understoodhereinafter, is a multiple ofb) in storage register 33 to signal b frombeam position input 29 and delivers the result to storage register 33.Hence, upon each clock pulse from clock pulse generator 49, signal be isincreased by the value of b.

Assuming there are six antenna elements A through A and hence sixcurrent generators, l-6, the operation of establishing the current forshifters 41, 42, etc. may be explained. Beam position input 29 isadjusted to provide a digital signal b indicative of a desired angle ofpropagation 0. Signal b is applied to binary adder 30. Assuming that cis initially zero, bi-

nary adder 30 adds the binary signal b to zero and delivers the result(which is, of course b to storage register 33. Clock pulse generator 49operates to produce a pulse to input 51 of storage register 33 to enablestorage resister 33 to store the signal from adder 30. Digital signal b,stored in the register is applied through output 34 to digital-to-analogconverter 35 which in turn produces a voltage V which corresponds todigital signal b received from storage register 33.

At the same time, the signal b in storage register 33 is applied tobinary adder 30 through input 36 and is added to signal b appearing atinput 31. The result, 2b is applied to the input of storage register 33.Clock pulse generator 49 produces another clock pulse to enable storageregister 33 to accept and store the new digital signal 2b. Also, as willbe more fully understood hereinafter, the same pulse from clock pulsegenerator 49 enables an appropriate one of the current generators toreceive the voltage from digital-to-analog converter 35. Beam step inputclock 55 produces a pulse to trigger single-shot multivibrator 57 whichin turn produces a pulse at lead 58 to enable current generator 1 toreceive a signal. Voltage V, appears at input 38 of current generator 1.During the next clock pulse from clock pulse generator 49, currentgenerator 1 is enabled by the pulse appearing at input 52. Thus, whencurrent generator 1 is enabled by a signal from clock 49 appearing atinput 52, and is triggered by a signal from clock 55 appearing at input58, the voltage V, occuring at input 38 operates on current generator 1so that current generator 1 produces a current having a valueproportional to the value of voltage V,. The current derived by thecurrent generator flows between lead 44 and ground 45 throughphase-shift coil 41. Thus, the phase shifter of antenna element A ofphase shifted by an amount dependent upon the value of voltage V whichin turn is dependent upon the beam position input binary signal, b. Whencurrent generator 1 is set, a signal is applied to lead 47 to enablecurrent generator 2 to accept an input. Thus, digital-to-analogconverter 35 will derive a new analog signal V dependent upon the valueof digital signal 2b, which analog signal V is applied to lead 37.During the next clock pulse from clock pulse generator 49, the digitalsignal appearing in storage register 33 is increased by b and currentgenerator 2 is set through input 33 to receive voltage V, through input39. Also, current generator 2 provides an output on lead 48 to enablethe next current generator.

The cycle continues until all current generators l-6 are set to providethe proper currents for the desired phase shifts.

From the foregoing, it can be understood that the binary signal storedin storage register 33 is of the general form be, where c is an integerwhich increases by one for each cycle of clock pulse generator 49.Hence, binary adder 30 adds b to be to derive (c+l b; the c+l becoming anew c.

Storage register 33 and binary adder 30 are designed to a capacity ofthe same number of bits. The voltage gain of the digital-to-analogconverter is adjusted to a value so that when the maximum storagecapacity of storage register 33 is reached, the voltage necessary toderive a 21r phase shift in each phase shifter is generated by generator35. Hence, if adder 30 attempts to provide a digital signal having anumber of binary characters which exceeds a 21) phase shift, only thatmuch of the binary signal which exceeds the Zn equivalent will betransferred to the digital-to-analog converter. For example, assumingthat a binary character of 1,000 (digital 8) would operate ondigital-to-analog converter 35 to produce a voltage which, when appliedto a current generator, would produce the current necessary forobtaining a Zn phase shift; and assuming b equaled binary 11 (digital3), storage register 33 would attempt to store the following tabulatedbinary signals:

TABLE 1v However, if a binary signal of 1,000 (digital 8 will produce a21: phase shift, which, of course is equal to a zero phase shift, abinary signal of 000 (digital 0) will produce the same results? Hence,in this case, the storage register could be constructed as to store onlythe last three binary bits (thereby dropping v any binary number inexcess of l l l-digital 7). Hence, in the example, the values of A ---Amay be represented as follows:

- TABLEV Since the ring or successive enabling relationship betweencurrent generator l-n ends with current generator n, additional settingof the current generators is not effectuated by additional pulses fromclock pulse generator. Hence, beam step input clock 55 periodicallyproduces a pulse to enable current generator 1 to be reset. Beam stepinput clock 55 may be related to binary adder 30 so as to clear anyinput appearing at input 36 on each clock pulse from clock 55, so uponinitiation of each setting cycle, by clock 55, binary adder, storageregister, and digital-to-analog converter operate on the first currentgenerator in identically the same manner as in the prior cycle.

Since clock 55 should operate at a rate less than the rate of the entirecycle, it is desirable that the frequency of clock 55 be less than orequal to l/ n times the frequency of clock pulse generator 49. Hence, inthe case of six antenna elements, the frequency of clock 55 will be lessthan one-sixth the frequency of clock pulse generator 49.

The present invention thus provides a cyclic beam control circuit forcontrolling the propagation direction for an antenna array. The cyclicbeam control network in accordance with the present invention isparticularly useful for controlling the phase shifters described in thesaid Chalfin et a]. application.

This invention is not to be limited by the embodiment shown in thedrawings and described in the description, which is given by way ofexample and not of limitation.

What I claim is:

1. Apparatus for controlling a plurality of electrically controllabledelay devices for an array of a plurality of antennav elements so thatthe antenna elements will propagate electromagnetic radiation in adesired direction, said apparatus comprising: adding means for addingdigital signals, said adding means having a first input adapted toreceive a digital signal representative of the desired direction ofpropagation of:

electromagnetic radiation by said array of antenna elements, said addingmeans having a second input and having an output, said adding meansbeing capable of adding a digital signal appearing at said first inputto a digital signal appearing at said second input; clock meansproviding a periodic signal; storage means connected to the output ofsaid adding means and to said clock means for storing the sum of thedigital signals upon receiving a periodic signal; means connecting theoutput of said storage means to the second input of said adding means;converter means connected to the output of said storage means forconverting the digital signal in said storage means to an analog signal;control means connected to said converter means for controlling each ofsaid delay devices and means connecting said control means to said clockmeans to periodically and successively operate said control means uponeach periodic signal to enable successive control of each of said delaydevices.

2. Apparatus according to claim 1 wherein said control means comprises aplurality of control devices each having a first input connected to theoutput of said converter means, each of said control devices beingoperable to control a respective delay device by an amount dependentupon the analog signal from said converter means for successivelyoperating the control devices.

3. Apparatus according to claim 2 wherein said last-named meanscomprises a first enable input to each of said control devices connectedto said clock means, and a second enable input to each of said controldevices, the second enable input to the first control device beingconnected to a control source and the second enable input to eachsuccessive control device being connected to an enable output of theprevious control device so that each control device is enabled uponsuccessful operation of the prior control device.

4. Apparatus according to claim 3 wherein said control source comprisesa second clock means.

5. Apparatus according to claim 4 wherein the delay devices arecurrent-operable and said control devices are current generators.

6. Apparatus according to claim 4 wherein there are n number of delaydevices and n number ofcontrol devices, said second clock means having afrequency not greater than l/n times the frequency of the first clockmeans.

7. A control circuit for controlling a plurality of load devicescomprising: a binary adder having a first input adapted to receive adigital signal indicative of a desired control function, a second inputand an output, said binary adder being capable of adding a binary signalat the first input and applying the sum to the output; a storageregister having an input connected to the output of said binary adderand having an output connected to the second input of said binary adder;a clock pulse generator connected to an input of said storage registerto enable said storage register to store the binary signal from saidbinary adder; a digital-to-analog converter having an input connected tothe output of said storage register and having an output; a plurality ofcurrent generators each having an input connected to the output of saiddigital-to-analog con verter sand each having a first enable inputconnected to said clock pulse generator and each having a second enableinput, some of said current generators having an enable output; a sourceof clock pulses connected to the second enable input of one of saidcurrent generators. the second enable input of each successive currentgenerator being connected to the enable output of the previous currentgenerator whereby the current generators are arranged in ring relation;and means connecting the output of each current generator to a respec've load device.

1. Apparatus for controlling a plurality of electrically controllabledelay devices for an array of a plurality of antenna elements so thatthe antenna elements will propagate electromagnetic radiation in adesired direction, said apparatus comprising: adding means for addingdigital signals, said adding means having a first input adapted toreceive a digital signal representative of the desired direction ofpropagation of electromagnetic radiation by said array of antennaelements, said adding means having a second input and having an output,said adding means being capable of adding a digital signal appearing atsaid first input to a digital signal appearing at said second input;clock means providing a periodic signal; storage means connected to theoutput of said adding means and to said clock means for storing the sUmof the digital signals upon receiving a periodic signal; meansconnecting the output of said storage means to the second input of saidadding means; converter means connected to the output of said storagemeans for converting the digital signal in said storage means to ananalog signal; control means connected to said converter means forcontrolling each of said delay devices and means connecting said controlmeans to said clock means to periodically and successively operate saidcontrol means upon each periodic signal to enable successive control ofeach of said delay devices.
 2. Apparatus according to claim 1 whereinsaid control means comprises a plurality of control devices each havinga first input connected to the output of said converter means, each ofsaid control devices being operable to control a respective delay deviceby an amount dependent upon the analog signal from said converter meansfor successively operating the control devices.
 3. Apparatus accordingto claim 2 wherein said last-named means comprises a first enable inputto each of said control devices connected to said clock means, and asecond enable input to each of said control devices, the second enableinput to the first control device being connected to a control sourceand the second enable input to each successive control device beingconnected to an enable output of the previous control device so thateach control device is enabled upon successful operation of the priorcontrol device.
 4. Apparatus according to claim 3 wherein said controlsource comprises a second clock means.
 5. Apparatus according to claim 4wherein the delay devices are current-operable and said control devicesare current generators.
 6. Apparatus according to claim 4 wherein thereare n number of delay devices and n number of control devices, saidsecond clock means having a frequency not greater than 1/n times thefrequency of the first clock means.
 7. A control circuit for controllinga plurality of load devices comprising: a binary adder having a firstinput adapted to receive a digital signal indicative of a desiredcontrol function, a second input and an output, said binary adder beingcapable of adding a binary signal at the first input and applying thesum to the output; a storage register having an input connected to theoutput of said binary adder and having an output connected to the secondinput of said binary adder; a clock pulse generator connected to aninput of said storage register to enable said storage register to storethe binary signal from said binary adder; a digital-to-analog converterhaving an input connected to the output of said storage register andhaving an output; a plurality of current generators each having an inputconnected to the output of said digital-to-analog converter sand eachhaving a first enable input connected to said clock pulse generator andeach having a second enable input, some of said current generatorshaving an enable output; a source of clock pulses connected to thesecond enable input of one of said current generators, the second enableinput of each successive current generator being connected to the enableoutput of the previous current generator whereby the current generatorsare arranged in ring relation; and means connecting the output of eachcurrent generator to a respective load device.